oa Evidence for the Long-term Barrier Integrity of Ordovician Rocks – The Deep Geologic Repository Project, Ontario, Canada

The Nuclear Waste Management Organization in late 2006 initiated geoscientific investigations at the Bruce Nuclear site near Tiverton, Ontario, Canada, to verify suitability for development of a Deep Geologic Repository for long-term management of Low & Intermediate Level Radioactive Waste generated at Ontario Power Generation owned facilities. The Bruce Nuclear site, located on the eastern flank of the Michigan Basin, is underlain by ca. 840 m of Cambrian to Devonian age sediments that lie unconformably on the crystalline Shield. The DGR, as envisioned, would be excavated at a depth of 680 m within the massive Cobourg Formation, an Ordovician argillaceous limestone that is overlain by ca. 200 m of Ordovician shale. Field and laboratory studies conducted as part of a deep borehole drilling, coring, testing and instrumentation program are yielding evidence of an ancient, diffusion dominant groundwater regime that is resilient to repeated glacial perturbations. This evidence includes measurements of extraordinarily low rock mass hydraulic conductivities(≤10-12 m sec-1), matrix porosities (0.01-0.08) and diffusivities (Dp≤10-11 m2 sec-1), and observation of anomalously depressed environmental heads (ca. 250 m) and vertical environmental tracer distributions within the Ordovician sediments. This presentation describes program results relevant to understanding groundwater regime stability and DGR safety.